Conventionally, an electrode for a lithium ion secondary cell is produced by applying a compound, obtained by dispersing an active material in a solvent together with a binder and a conductive material, on a current collector and then drying the compound. As the ratio of the binder and the conductive material in the electrode is lower, the cell capacitance per unit volume is larger and thus a higher capacitance cell is obtained. Therefore, it has been studied to produce an electrode without using a binder.
As an example of a method for producing an electrode without using a binder, it has been proposed to use an aerosol deposition method (hereinafter, referred to simply as an “AD method”) to produce an electrode for a lithium ion secondary cell. Herein, “aerosol” means microparticles of a solid or a liquid floating in a gas. The “AD method” is a film formation method of generating an aerosol containing particles of a material and jetting the aerosol from a nozzle toward a substrate to deposit the particles. With the AD method, material particles jetted at a high speed collide against the substrate or the material particles already deposited, and a new surface is generated. In addition, the material particles themselves are each crushed at the time of collision, and a new surface is generated on each material particle. By a mechanochemical reaction that such newly generated surfaces adhere to one another, the particles bond to one another and also to the substrate. As a result, a film is formed on the substrate. The AD method is useful as a technology for forming various types of films in addition to an electrode.
With the AD method, the film formation rate varies by various factors such as the concentration and the jetting speed of the aerosol, the scanning rate of the nozzle and the like. It is difficult to keep the film quality constant because the film formation rate is likely to vary, and a film of a desired thickness cannot be formed merely by adjusting the time of film formation. The AD method is a relatively new technology and so how to adjust the film quality and the film thickness has not been sufficiently studied.
Patent Document 1, for example, describes a method called a “gas deposition method” as a film formation method similar to the AD method. The AD method forms an aerosol from powders having a diameter of sub-microns to several microns, carries the aerosol by a carrier gas and forms a film using a mechanochemical reaction, whereas the gas deposition method synthesizes microparticles in a gas phase, carries the microparticles to a substrate by a carrier gas and deposits the microparticles. In general, the microparticles used as a material is generated by vaporizing and then solidifying metal particles.
Patent Document 2, for example, discloses a method for adjusting the thickness of a film formed by the AD method, by which an aerosol containing ceramic particles is generated, the amount of the ceramic microparticles in the aerosol is sensed by a sensor, and the amount is fed back to a control section in a generator.
Patent Document 3 discloses a gas deposition method, by which a part of super-microparticles which have formed an aerosol is introduced to a particle measurement device, either one or both of the particle diameter distribution or the concentration of the super-microparticles are measured by the particle measurement device, and either one or both of the flow rate of the carrier gas and the heating energy are controlled.
Patent Document 4 discloses a gas deposition method, by which particles of a constant quantity are supplied to a space in a second chamber using particle supply means to form an aerosol having a certain particle concentration.    Patent Document 1: Japanese Laid-Open Patent Publication No. 6-128728    Patent Document 2: Japanese Laid-Open Patent Publication No. 2001-348659    Patent Document 3: Japanese Laid-Open Patent Publication No. 2003-313656    Patent Document 4: Japanese Laid-Open Patent Publication No. 2006-200013